U.S. patent application number 12/250062 was filed with the patent office on 2010-04-15 for shape memory polyurethane foam for downhole sand control filtration devices.
This patent application is currently assigned to BAKER HUGHES INCORPORATED. Invention is credited to Ping Duan, Paul McElfresh.
Application Number | 20100089565 12/250062 |
Document ID | / |
Family ID | 42097823 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100089565 |
Kind Code |
A1 |
Duan; Ping ; et al. |
April 15, 2010 |
Shape Memory Polyurethane Foam for Downhole Sand Control Filtration
Devices
Abstract
Filtration devices may include a shape-memory material having a
compressed run-in position or shape and an original expanded
position or shape. The shape-memory material may include an open
cell porous rigid polyurethane foam material held in the compressed
run-in position at the temperature below glass transition
temperature (T.sub.g). The foam material in its compressed run-in
position may be covered with a fluid-dissolvable polymeric film
and/or a layer of fluid-degradable plastic. Once filtration devices
are in place in downhole and are contacted by the fluid for a given
amount of time at temperature, the devices may expand and totally
conform to the borehole to prevent the production of undesirable
solids from the formation.
Inventors: |
Duan; Ping; (Spring, TX)
; McElfresh; Paul; (Spring, TX) |
Correspondence
Address: |
Mossman, Kumar and Tyler, PC
P.O. Box 421239
Houston
TX
77242
US
|
Assignee: |
BAKER HUGHES INCORPORATED
Houston
TX
|
Family ID: |
42097823 |
Appl. No.: |
12/250062 |
Filed: |
October 13, 2008 |
Current U.S.
Class: |
166/51 ; 166/278;
264/40.4; 264/48 |
Current CPC
Class: |
E21B 43/082
20130101 |
Class at
Publication: |
166/51 ; 264/48;
264/40.4; 166/278 |
International
Class: |
E21B 43/04 20060101
E21B043/04; B29C 43/32 20060101 B29C043/32; B29C 43/52 20060101
B29C043/52; B29C 43/58 20060101 B29C043/58 |
Claims
1. A wellbore filtration device comprising: a shape-memory porous
material, the shape-memory porous material having a compressed
position and an expanded position, where the shape-memory porous
material is maintained in the compressed position at a temperature
below its glass transition temperature, where the shape-memory
porous material expands from its compressed position to its
expanded position when it is heated to a temperature above its
glass transition temperature.
2. The filtration device of claim 1, wherein the shape-memory
porous material comprises a polyurethane foam.
3. The filtration device of claim 2 where the polyurethane foam
material is formed by mixing a polycarbonate polyol with a
polyisocyanate.
4. The filtration device of claim 1, wherein the shape-memory
porous material has an outer surface covered with a covering
selected from the group consisting of a fluid-dissolvable polymeric
film, a layer of thermally fluid-degradable plastic, and a
combination thereof.
5. A method of manufacturing a wellbore filtration device, the
method comprising: (a) mixing an isocyanate portion comprising an
isocyanate with a polyol portion comprising a polyol to form an
open-cell polyurethane foam material having an original expanded
volume; (b) compressing the polyurethane foam material at a
temperature above its glass transition temperature T.sub.g to
reduce the original expanded volume to a compressed run-in volume;
(c) lowering the temperature of the compressed polyurethane foam
material to a temperature below T.sub.g where the polyurethane foam
material maintains its compressed run-in volume; and (d) covering
an outer surface of the compressed polyurethane foam material with
a covering selected from the group consisting of a
fluid-dissolvable polymeric film, a layer of thermally
fluid-degradable plastic, and a combination thereof.
6. The method of claim 5, wherein the polyol portion comprises a
mixture of polyol and water.
7. The method of claim 5 where the polyol portion comprises a
polycarbonate polyol.
8. The method of claim 5, wherein the polyol portion comprises a
chain extender.
9. The method of claim 8, wherein the chain extender comprises an
aromatic diamine.
10. The method of claim 5, wherein the polyol portion comprises
water, a chain extender and a catalyst selected from the group
consisting of amine-based catalysts, metal-based catalysts and
mixtures thereof.
11. The method of claim 5, wherein the polyol portion comprises
water, a chain extender, a catalyst, and a surfactant.
12. The method of claim 11, wherein the surfactant further
comprises a cell opener.
13. The method of claim 5, wherein the polyol portion is preheated
to at least 90.degree. C. prior to being combined with the
isocyanate portion.
14. The method of claim 5, wherein step (a) further comprises
curing the polyurethane foam material in a mold and then heating
the polyurethane foam material at a temperature greater than
110.degree. C.
15. The method of claim 5, wherein step (a) comprises mixing
equivalent weights of the isocyanate portion and the polyol
portion.
16. The method of claim 5, wherein step (a) comprises mixing the
isocyanate portion and the polyol portion in a mixer for at least
about 10 seconds and curing the polyurethane foam material in a
mold at room temperature for at least about 2 hours.
17. The method of claim 16, wherein step (a) further comprises,
after curing the polyurethane foam material, heating the
polyurethane foam material at a temperature of at least about
110.degree. C. for at least about 8 hours.
18. A method of installing a wellbore filtration device on a
downhole tool in a formation, the method comprising: (a) securing a
downhole tool to a string of perforated tubing, the downhole tool
comprising a filtration device comprising a shape-memory porous
material, the shape-memory porous material having a compressed
run-in position and an original expanded position, wherein the
shape-memory porous material is maintained in the compressed run-in
position below a glass transition temperature of the shape-memory
porous material, the shape-memory porous material in its compressed
run-in position having an outer surface with a covering selected
from the group consisting of a fluid-dissolvable polymeric film, a
layer of fluid-degradable polyurethane plastic or fluid-degradable
polyester plastic, and a combination thereof; (b) running the
downhole tool in a wellbore; (c) contacting the covering and the
shape-memory porous material with a fluid; (d) removing the
covering with the fluid; (e) expanding the shape-memory porous
material from the compressed run-in position to an expanded
position against the wellbore.
19. The method of claim 18 further comprising (f) producing
hydrocarbons from the formation through the wellbore where the
shape-memory porous material in the expanded position prevents the
undesirable production of solids from the formation but allows the
desirable production of hydrocarbons.
20. The method of claim 18 where the fluid is water.
21. The method of claim 18 where the fluid is oil.
22. The method of claim 18 where the shape-memory porous material
comprises polyurethane formed by mixing a polycarbonate polyol with
a polyisocyanate.
Description
TECHNICAL FIELD
[0001] The present invention relates to filtration devices used in
oil and gas wellbores to prevent the production of undesirable
solids from the formation, and more particularly relates to
filtration devices having shape-memory porous materials that remain
in a compressed state during run-in; once the filtration devices
are in place downhole and are contacted by a fluid for a given
amount of time at temperature, the devices can expand and totally
conform to the borehole.
TECHNICAL BACKGROUND
[0002] Various sand control methods by gravel packing outside of
down-hole screens are known in the art. Gravels are introduced from
the surface to fill the annular space between outside the screen
and the inner wall surface of a wellbore to prevent the production
of undesirable solids from the formation. More recently, it was
thought that the need for gravel packing could be eliminated if a
screen or screens could be expandable to the inner wall surface of
a wellbore. Problems arose with the screen expansion technique as a
replacement for gravel packing because of wellbore shape
irregularities. U.S. Pat. No. 7,013,979 disclosed a totally
conforming expandable screen to conform the borehole irregular
shape. This conforming expandable screen consists of a
self-swelling material that is capable of expansion of its volume
by contacting well fluids. U.S. Pat. No. 7,318,481 disclosed a
self-conforming expandable screen which comprises of thermosetting
open cell shape-memory polymeric foam. The foam material
composition is formulated to achieve the desired transition
temperature slightly below the anticipated downhole temperature at
the depth at which the assembly will be used. This causes the
conforming foam to expand at the temperature found at the desired
depth, and to remain expanded against the borehole wall.
[0003] There are many types of polymeric foam commercially
available such as natural rubber foam, vinyl rubber foam,
polyethylene foam, neoprene rubber foam, silicone rubber foam,
polyurethane foam, VITON.RTM. rubber foam, polyimide foam, etc.
Most of these foams are cell-closed, soft and lack of structural
strength to be used in the downhole conditions. Some of these foams
such as rigid polyurethane foam are hard but very brittle. In
addition, conventional polyurethane foams which are generally made
from polyethers or polyesters lack thermal stability and the
necessary chemical capabilities. Consequently these foams are
undesirably quickly destroyed in the downhole fluids, especially at
an elevated temperature.
[0004] It would thus be very desirable and important to discover a
method and device for deploying an element at a particular location
downhole to prevent the production of undesirable solids from the
formation and allow only the desired hydrocarbon fluids to flow
through.
SUMMARY
[0005] There is provided, in one form, a wellbore filtration device
that involves a shape-memory porous material. The shape-memory
porous material has a compressed position and an expanded position.
The shape-memory porous material is maintained in its compressed
position at a temperature below its glass transition temperature.
The shape-memory porous material expands from its compressed
position to its expanded position when it is heated to a
temperature above its glass transition temperature.
[0006] In another non-limiting embodiment there is provided a
method of manufacturing a wellbore filtration device. The method
involves mixing an isocyanate portion that contains an isocyanate
with a polyol portion that contains a polyol to form an open-cell
polyurethane foam material. The open-cell polyurethane foam
material has an original expanded volume. The polyurethane foam
material is compressed at a temperature above its glass transition
temperature T.sub.g to reduce the original expanded volume to a
compressed run-in volume. The temperature of the compressed
polyurethane foam material is lowered to a temperature below
T.sub.g, but the polyurethane foam material maintains its
compressed run-in volume. The method further comprises covering the
outer surface of the compressed polyurethane foam material with a
covering that may be a fluid-dissolvable polymeric film and/or a
layer of thermally fluid-degradable plastic.
[0007] Further there is provided in a different, non-restrictive
version a method of installing a wellbore filtration device on a
downhole tool in a formation. The method involves securing a
downhole tool to a string of perforated tubing. The downhole tool
has a filtration device with a shape-memory porous material. The
shape-memory porous material has a compressed run-in position and
an original expanded position. The shape-memory porous material is
maintained in the compressed run-in position below a glass
transition temperature of the shape-memory porous material. The
shape-memory porous material in its compressed run-in position has
an outer surface with a covering. The covering may a
fluid-dissolvable polymeric film and/or a layer of thermally
fluid-degradable plastic. The downhole tool is run into a wellbore.
The covering and the shape-memory porous material is contacted with
a fluid. The covering is removed by the fluid. The shape-memory
porous material expands from its compressed run-in position to an
expanded position against the wellbore. In this way it serves a
filtration function by preventing undesirable solids from being
produced while permitting desirable hydrocarbons to flow through
the filtration device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic, cross-section view of a filtration
device which bears a shape-memory porous material in its
compressed, run-in thickness or volume, having thereover a
degradable delaying film, covering or coating material; and
[0009] FIG. 2 is a schematic, cross-section view of the filtration
device of FIG. 1 where the degradable delaying film, covering or
coating material has been removed and the shape-memory porous
material has been permitted to expand or deploy so that it firmly
engages and fits to the inner wall surface of the well-bore casing
to prevent the production of undesirable solids from the formation,
allowing only hydrocarbon fluids to flow therethrough.
[0010] It will be appreciated that FIGS. 1 and 2 are simply
schematic illustrations which are not to scale and that the
relative sizes and proportions of different elements may be
exaggerated for clarity or emphasis.
DETAILED DESCRIPTION
[0011] Downhole tools and, in particular, filtration devices for
downhole sand control, are disclosed herein. The filtration devices
include one or more shape-memory materials that are run into the
wellbore in a compressed shape or position. The shape-memory
material remains in the compressed shape induced on it after
manufacture at surface temperature or at wellbore temperature
during run-in. After the filtration device having the shape-memory
material is placed at the desired location within the well, the
shape-memory material is allowed to expand to its pre-compressed
shape, i.e., its original, manufactured shape, at downhole
temperature at a given amount of time. The expanded shape or set
position, therefore, is the shape of the shape-memory material
after it is manufactured and before it is compressed. In other
words, the shape-memory material possesses hibernated shape-memory
that provides a shape to which the shape-memory material naturally
takes after its manufacturing when it is deployed downhole.
[0012] As a result of the shape-memory material being expanded to
its set position, the completely open cell porous material can
prevent production of undesirable solids from the formation and
allow only desired hydrocarbon fluids to flow through the
filtration device. The completely open cell porous material or foam
is made in one non-limiting embodiment from one or more
polycarbonate polyol and a modified diphenylmethane diisocyanate
(MDI), as well as other additives including, but not necessarily
limited to, blowing agents, molecular cross linkers, chain
extenders, surfactants, colorants and catalysts. The foam cell pore
size, size distribution and cell openness may be achieved by
formulating different components and by controlling processing
conditions in such a way that only desired hydrocarbon fluids are
allowed to flow through and undesirable solids from the formation
are prevented from being produced.
[0013] The shape-memory polyurethane foam material is capable of
being mechanically compressed substantially, e.g., 20.about.30% of
its original volume, at temperatures above its glass transition
temperature (T.sub.g) at which the material becomes soft. While
still being compressed, the material is cooled down well below its
T.sub.g, or cooled down to room or ambient temperature, and it is
able to remain at compressed state even after the applied
compressive force is removed. When the material is heated near or
above its T.sub.g, it is capable of recovery to its original
un-compressed state or shape. In other words, the shape-memory
material possesses hibernated shape-memory that provides a shape to
which the shape-memory material naturally takes after its
manufacturing. The compositions of polyurethane foam are able to be
formulated to achieve desired glass transition temperatures which
are suitable for the downhole applications, where deployment can be
controlled for temperatures below T.sub.g of filtration devices at
the depth at which the assembly will be used.
[0014] Generally, polyurethane elastomer or polyurethane foam is
considered poor in thermal stability and hydrolysis resistance,
especially when it is made from polyether or polyester. It has been
discovered herein that the thermal stability and hydrolysis
resistance are significantly improved when the polyurethane is made
from polycarbonate polyols and MDI diisocyanates. There are many
polycarbonate polyols commercially available such as Desmophen
C1200 and Desmophen 2200 from Bayer, Poly-CD 220 from Arch
Chemicals, PC-1733, PC-1667 and PC-1122 from Stahl USA. In one
non-limiting embodiment, the polycarbonate polyol PC-1667 or
poly(cycloaliphatic carbonate) is suitable because it shows
exceptional thermal and hydrolytic stability when it is used to
make polyurethane. In addition, the polyurethane made from
poly(cycloaliphatic carbonate) is hard and tough. The compositions
of polyurethane foam are able to be formulated to achieve different
glass transition temperatures within the range from 60.degree. C.
to 170.degree. C., which is especially suitable to meet most
downhole application temperature requirements.
[0015] In one specific non-limiting embodiment, the shape-memory
material is a polyurethane foam material that is extremely tough
and strong and that is capable of being compressed and returned to
substantially its original expanded shape. The T.sub.g of the
shape-memory polyurethane foam is about 94.4.degree. C. and it is
compressed by mechanical force at 125.degree. C., in another
non-limiting embodiment. While still in compressed state, the
material is cooled down to room temperature. The shape-memory
polyurethane foam is able to remain in the compressed state even
after applied mechanical force is removed. When material is heated
to about 88.degree. C., it is able to return to its original shape
within 20 minutes. However, when the same material is heated to a
lower temperature such as 65.degree. C. for about 40 hours, it
remains in the compressed state and does not change its shape.
[0016] Ideally, when shape-memory polyurethane foam is used as a
filtration media for downhole sand control applications, it is
preferred that the filtration device remains in a compressed state
during run-in until it reaches to the desired downhole location.
Usually, downhole tools traveling from surface to the desired
downhole location take hours or days. When the temperature is high
enough during run-in, the filtration devices made from the
shape-memory polyurethane foam could start to expand. To avoid
undesired early expansion during run-in, delaying methods may or
must be taking into consideration. In one specific, but
non-limiting embodiment, poly(vinyl alcohol) (PVA) film is used to
wrap or cover the outside surface of filtration devices made from
shape-memory polyurethane foam to prevent expansion during run-in.
Once filtration devices are in place in downhole for a given amount
of time at temperature, the PVA film is capable of being dissolved
in the water, emulsions or other downhole fluids and, after such
exposure, the shape-memory filtration devices can expand and
totally conform to the bore hole. In another alternate, but
non-restrictive specific embodiment, the filtration devices made
from the shape-memory polyurethane foam may be coated with a
thermally fluid-degradable rigid plastic such as polyester
polyurethane plastic and polyester plastic. By the term "thermally
fluid-degradable plastic" is meant any rigid solid polymer film,
coating or covering that is degradable when it is subjected to a
fluid, e.g. water or hydrocarbon or combination thereof and heat.
The covering is formulated to be degradable within a particular
temperature range to meet the required application or downhole
temperature at the required period of time (e.g. hours or days)
during run-in. The thickness of delay covering and the type of
degradable plastics may be selected to be able to keep filtration
devices of shape-memory polyurethane foam from expansion during
run-in. Once the filtration device is in place downhole for a given
amount of time at temperature, these degradable plastics decompose
and which allows the filtration devices to expand to the inner wall
of bore hole. In other words, the covering that inhibits or
prevents the shape-memory porous material from returning to its
expanded position or being prematurely deployed may be removed by
dissolving, e.g. in an aqueous or hydrocarbon fluid, or by thermal
degradation or hydrolysis, with or without the application of heat,
in another non-limiting example, destruction of the crosslinks
between polymer chains of the material that makes up the
covering.
[0017] The polyurethane foam material may be formed by combining
two separate portions of chemical reactants and reacting them
together. These two separate portions are referred to herein as the
isocyanate portion and polyol portion. The isocyanate portion may
comprise a modified isocyanate (MI) or a modified diphenylmethane
diisocyanate (MDI) based monomeric diisocyanate or polyisocyanate.
The polyol portion may include, but not necessarily be limited to,
a polyether, polyester or polycarbonate-based di- or
multifunctional hydroxylended prepolymer.
[0018] Water may be included as part of the polyol portion and may
act as a blowing agent to provide a porous foam structure when
carbon dioxide is generated from the reaction with the isocyanate
and water when the isocyanate portion and the polyol portion are
combined.
[0019] In one non-restrictive embodiment, the isocyanate portion
may contain modified MDI MONDUR PC sold by Bayer or MDI prepolymer
LUPRANATE 5040 sold by BASF, and the polyol portion may contain (1)
a poly(cycloaliphatic carbonate) polyol sold by Stahl USA under the
commercial name PC-1667; (2) a tri-functional hydroxyl cross linker
trimethylolpropane (TMP) sold by Alfa Aesar; (3) an aromatic
diamine chain extender dimethylthiotoluenediamine (DMTDA) sold by
Albemarle under the commercial name ETHACURE 300; (4) a catalyst
sold by Air Products under the commercial name POLYCAT 77; (5) a
surfactant sold by Air Products under the commercial name DABCO
DC198; (6) a cell opener sold by Degussa under the commercial name
ORTEGOL 501, (7) a colorant sold by Milliken Chemical under the
commercial name REACTINT Violet X80LT; and (8) water.
[0020] The ratio between two separate portions of chemical
reactants which are referred to herein as the isocyanate portion
and polyol portion may, in one non-limiting embodiment, be
chemically balanced close to 1:1 according to their respective
equivalent weights. The equivalent weight of the isocyanate portion
is calculated from the percentage of NCO (isocyanate) content which
is referred to herein as the modified MDI MONDUR PC and contains
25.8% NCO by weight. Other isocyanates such as MDI prepolymer
Lupranate 5040 sold by BASF contains 26.3% NCO by weight are also
acceptable. The equivalent weight of the polyol portion is
calculated by adding the equivalent weights of all reactive
components together in the polyol portion, which includes polyol,
e.g., PC-1667, water, molecular cross linker, e.g., TMP, and chain
extender, e.g., DMTDA. The glass transition temperature of the
finished polyurethane foam may be adjustable via different
combinations of isocyanate and polyol. In general, the more
isocyanate portion, the higher the T.sub.g that is obtained.
[0021] The chain extender, dimethylthiotoluenediamine (DMTDA) sold
by Albemarle under the commercial name ETHACURE 300, is a liquid
aromatic di-amine curative that provides enhanced high temperature
properties. Other suitable chain extenders include but are not
limited to 4,4'-Methylene bis (2-chloroaniline), "MOCA", sold by
Chemtura under the commercial name VIBRA-CURE.RTM. A 133 HS, and
trimethylene glycol di-p-aminobenzoate, "MCDEA", sold by Air
Products under the commercial name VERSALINK 740M. In certain
embodiments, either amine-based or metal-based catalysts are
included to achieve good properties of polyurethane foam materials.
Such catalysts are commercially available from companies such as
Air Products. Suitable catalysts that provide especially good
properties of polyurethane foam materials include, but are not
necessarily limited to, pentamethyidipropylenetriamine, an
amine-based catalyst sold under the commercial name POLYCAT 77 by
Air Products, and dibutyltindilaurate, a metal-based catalyst sold
under the commercial name DABCO T-12 by Air Products.
[0022] A small amount of surfactant, e.g., 0.5% of total weight,
such as the surfactant sold under the commercial name DABCO DC-198
by Air Products and a small amount of cell opener, e.g., 0.5% of
total weight, such as the cell opener sold under the commercial
names ORTEGOL 500, ORTEGOL 501, TEGOSTAB B8935, TEGOSTAB B8871, and
TEGOSTAB B8934 by Degussa may be added into the formulations to
control foam cell structure, distribution and openness. DABCO
DC-198 is a silicone-based surfactant from Air Products. Other
suitable surfactants include, but are not necessarily limited to,
fluorosurfactants sold by DuPont under commercial names ZONYL 8857A
and ZONYL FSO-100. Colorant may be added in the polyol portion to
provide desired color in the finished products. Such colorants are
commercially available from companies such as Milliken Chemical
which sells suitable colorants under the commercial name
REACTINT.
[0023] After the isocyanate portion and the polyol portion are
prepared, they are combined or mixed together at a desired
temperature. The temperature at which the two portions are combined
affects the degree of cell size within the resultant polyurethane
foam material. For example, higher temperatures of the mixture
provide larger cell size while lower temperatures of the mixture
provide smaller cell size.
[0024] In one particular, but non-restrictive embodiment, the
polyol portion including poly(cycloaliphatic carbonate) and other
additives such as cross linker, chain extender, surfactant, cell
opener, colorant, water, and catalyst is pre-heated to 90.degree.
C. before being combined with the isocyanate portion. The
isocyanate portion is combined with the polyol portion and a
foaming reaction is immediately initiated and the mixture's
viscosity increases rapidly.
[0025] Due to the high viscosity of the mixture and the fast
reaction rate, a suitable mixer is recommended to form the
polyurethane foam material. Although there are many commercially
available fully automatic mixers specially designed for two-part
polyurethane foam processing, it is found that mixers such as
KITCHENAID.RTM. type mixers with single or double blades work
particularly well. In large-scale mixing, eggbeater mixers and
drill presses have been found to work particularly well.
[0026] In mixing the isocyanate and polyol portions, the amount of
isocyanate and polyol included in the mixture should be chemically
balanced according to their equivalent weight. In one specific
non-limiting embodiment, 5% more isocyanate by equivalent weight is
combined with the polyol portion.
[0027] In one embodiment, the ratio between isocyanate and
polycarbonate polyol is about 1:1 by weight. The polyol portion may
be formed by 46.0 g of PC-1667 poly(cycloaliphatic carbonate)
polycarbonate combined with 2.3 g of TMP cross-linker, 3.6 g of
DMTDA chain extender, 0.9 g DABCO DC-198 surfactant, 0.4 g of
ORTEGOL 501 cell opener, 0.1 g of REACTINT Violet X80LT colorant,
0.01 g of POLYCAT 77 catalyst, and 0.7 g of water blowing agent to
form the polyol portion. The polyol portion is preheated to
90.degree. C. and mixed in a KITCHENAID .RTM. type single blade
mixer with 46.0 g of MDI MONDUR PC. As will be recognized by
persons of ordinary skill in the art, these formulations can be
scaled-up to form larger volumes of this shape-memory material.
[0028] The mixture containing the isocyanate portion and the polyol
portion may be mixed for about 10 seconds and then poured into a
mold and the mold immediately closed by placing a top metal plate
thereon. Due to the significant amount pressure generated by
foaming process, a C-clamp may be used to hold the top metal plate
and mold together to prevent any leakage of mixture. After
approximately 2 hours at room temperature, the polyurethane foam
material including a mold and a C-clamp may be placed inside an
oven and "post-cured" at a temperature of 110.degree. C. for
approximately 8 hours so that the polyurethane foam material
reaches its full strength. After cooled down to room temperature,
the polyurethane foam material is sufficiently cured such that the
mold may be removed. Thereafter, the polyurethane foam material at
this stage will, almost always, include a layer of "skin" on the
outside surface of the polyurethane foam. The "skin" is a layer of
solid polyurethane plastic formed when the mixture contacts with
the mold surface. It has been found that the thickness of the skin
depends on the concentration of water added to the mixture. Excess
water content decreases the thickness of the skin and insufficient
water content increases the thickness of the skin. In one
non-limiting explanation, the formation of the skin is believed to
be due to the reaction between the isocyanate in the mixture and
the moisture on the mold surface. Therefore, additional mechanic
conversion processes are needed to remove the skin, since in most
cases the skin is not porous to the passage of fluids therethrough.
Tools such as band saws, miter saws, core saws, hack saws and
lathes may be used to remove the skin. After removing the skin from
the polyurethane foam material, it will have a full open cell
structure, that is, rigid, strong and tough.
[0029] At this point, the polyurethane foam material is in its
original, expanded shape having an original, or expanded,
thickness. The T.sub.g of the polyurethane foam material is
measured by Dynamic Mechanical Analysis (DMA) as 94.4.degree. C.
from the peak of loss modulus, G''. The polyurethane foam material
may be capable of being mechanically compressed to at least 25% of
original thickness or volume at temperature 125.0.degree. C. in a
confining mold. While still in the compressed state, the material
is cooled down to room temperature. The shape-memory polyurethane
foam is able to remain in the compressed state even after applied
mechanical force is removed. When the material is heated to about
88.degree. C., in one non-restrictive version, it is able to return
to its original shape within 20 minutes. However, when the same
material is heated to about 65.degree. C. for about 40 hours, it
does not expand or change its shape at all.
[0030] In another non-limiting embodiment, the ratio between
isocyanate and polycarbonate polyol is about 1.5:1 by weight. The
polyol portion may be formed by 34.1 g of PC-1667
poly(cycloaliphatic carbonate) polycarbonate combined with 2.3 g of
TMP cross linker, 10.4 g of DMTDA chain extender, 0.8 g DABCO
DC-198 surfactant, 0.4 g of ORTEGOL 501 cell opener, 0.1 g of
REACTINT Violet X80LT colorant, 0.01 g of POLYCAT 77 catalyst, and
0.7 g of water blowing agent to form the polyol portion. The polyol
portion is preheated to 90.degree. C. and mixed in a
KITCHENAID.RTM. type single blade mixer with 51.2 g of MDI MONDUR
PC. As will be recognized by persons of ordinary skill in the art,
these formulations can be scaled-up to form larger volumes of this
shape-memory material.
[0031] The mixture containing the isocyanate portion and the polyol
portion may be mixed for about 10 seconds and then poured into a
mold and the mold immediately closed by placing a top metal plate
thereon. Due to the significant amount pressure generated by
foaming process, a C-clamp or other device may be used to hold the
top metal plate and mold together to prevent any leakage of
mixture. After approximately 2 hours, the polyurethane foam
material including a mold and a C-clamp may be transferred into an
oven and "post-cured" at a temperature of 110.degree. C. for
approximately 8 hours so that the polyurethane foam material
reaches its full strength. After cooled down to room temperature,
the polyurethane foam material is sufficiently cured such that the
mold can be removed.
[0032] The T.sub.g of this polyurethane foam material may be
measured as 117.0.degree. C. by DMA from the peak of loss modulus,
G''.
[0033] As may be recognized, the polyurethane foam having more
isocyanate than polyol by weight results in higher glass transition
temperature. The polyurethane foam having less isocyanate than
polyol by weight results in lower T.sub.g. By formulating different
combinations of isocyanate and polyol, different glass transition
temperatures of shape-memory polyurethane foam may be achieved.
Compositions of a shape-memory polyurethane foam material having a
specific T.sub.g may be formulated based on actual downhole
deployment/application temperature. Usually, the T.sub.g of a
shape-memory polyurethane foam is designed about 20.degree. C.
higher than actual downhole deployment/application temperature.
Because the application temperature is lower than T.sub.g, the
material retains good mechanical properties.
[0034] In one non-restrictive embodiment, the shape-memory
polyurethane foam in tubular shape may be compressed under
hydraulic pressure above glass transition temperature, and then
cooled to a temperature well below the T.sub.g or room temperature
while it is still under compressing force. After the pressure is
removed, the shape-memory polyurethane foam is able to remain at
the compressed state or shape. The tubular compressed shape-memory
polyurethane material may then be tightly wrapped with (PVA) film
commercially available from Idroplax, S.r.l., Italy, under the
commercial name HT-350, in one non-limiting embodiment. In another
non-restrictive embodiment, the tubular compressed shape-memory
polyurethane material may be roll-coated with a layer of thermally
fluid-degradable polyurethane resin which is formed by combining 70
parts, by weight, of liquid isocyanate such as MONDUR PC from Bayer
and 30 parts, by weight, liquid polyester polyol such as FOMREZ 45
from Chemtura. In another non-limiting embodiment, the tubular
compressed shape-memory polyurethane foam material may be dipped
inside a pan containing the liquid polyurethane mixture while it is
slowly rotating. Within about 5 minutes, a layer of polyurethane
coating about 1.5 mm thick will be built up. Such a polyurethane
coating may be cured at room temperature for about 8 hours. In one
non-restrictive version, it is helpful if the material remains
rotating while it is under curing process to avoid any dripping of
resin. About 0.1% catalyst such as POLYCAT 77 from Air Products may
be added in the polyurethane mixture to accelerate curing
process.
[0035] With reference to FIGS. 1 and 2, in operation, the tubing
string 20 having filtration device 30 including a shape-memory
porous material 32 is run-in wellbore 50, which is defined by
wellbore casing 52, to the desired location. As shown in FIG. 1,
shape-memory material 32 has a compressed, run-in, thickness 34,
and an outside delay film, covering or coating 40. After a
sufficient amount of delaying film, covering or coating material 40
is dissolved or de-composed, i.e., after the delaying film,
covering or coating material 40 is dissolved or decomposed such
that the stored energy in the compressed shape-memory material 32
is greater than the compressive forces provided by the delaying
material, shape-memory porous material 32 expands from the run-in
or compressed position (FIG. 1) to the expanded or set position
(FIG. 2) having an expanded thickness 36. In so doing, shape-memory
material 32 engages with inner wall surface 54 of wellbore casing
52, and, thus, prevents the production of undesirable solids from
the formation, allows only hydrocarbon fluids flow through the
filtration device 30.
[0036] Further, when it is described herein that the filtration
device "totally conforms" to the borehole, what is meant is that
the shape-memory porous material expands or deploys to fill the
available space up to the borehole wall. The borehole wall will
limit the final, expanded shape of the shape-memory porous material
and in fact not permit it to expand to its original, expanded
position or shape. In this way however, the expanded or deployed
shape-memory material, being porous, will permit hydrocarbons to be
produced from a subterranean formation through the wellbore, but
will prevent or inhibit small or fine solids from being produced
since they will generally be too large to pass through the open
cells of the porous material.
[0037] It is to be understood that the invention is not limited to
the exact details of construction, operation, exact materials, or
embodiments shown and described, as modifications and equivalents
will be apparent to one skilled in the art. Accordingly, the
invention is therefore to be limited only by the scope of the
appended claims. Further, the specification is to be regarded in an
illustrative rather than a restrictive sense. For example, specific
combinations of components to make the polyurethane/urea
thermoplastic, specific downhole tool configurations and other
compositions, components and structures falling within the claimed
parameters, but not specifically identified or tried in a
particular method or apparatus, are anticipated to be within the
scope of this invention.
[0038] The terms "comprises" and "comprising" in the claims should
be interpreted to mean including, but not limited to, the recited
elements.
[0039] The present invention may suitably comprise, consist or
consist essentially of the elements disclosed and may be practiced
in the absence of an element not disclosed.
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